I've worked with unity builds a lot in my career. Rebuilding a unity module can be 90s-2minutes (plus linking), whereas a single file might only be 3-5 seconds

I've worked with unity builds a lot in my career. Rebuilding a unity module can be 90s-2minutes (plus linking), whereas a single file might only be 3-5 seconds on its own. The best possibility is if your build system can detect which files have changed and exclude them from unity builds, as this gives you the "slow path" the first time you change a file, but from then on you get the fast path behaviour.